It is critical before designing a new 4D survey to have a detailed understanding of what happened during the Baseline survey. Baseline data will be QC'd and analysed to look for anomalies that would either have an impact on the Monitor survey design or would give an insight into likely acquisition issues. This analysis will lead to an understanding of the options to be considered for the design phase.
Monitor Survey Design
Once the baseline data has been analysed and any issues understood, the focus moves to the monitor survey design. The geometry options will then be modeled and using 4D attribute analysis the expected repeatability will be computed. Typically the geometries that could be modelled can include:
- Conventional (various geometries)
- Hi-Res geometry
- Steerable cables
- Any other geometry required
Once the options are understood, decisions can be made to choose the appropriate balance between repeatability optimisation and project costs.
Monitor Survey Planning
Once we have a basic monitor survey design, the survey has to be planned in detail. This plan is formulated by considering both the original baseline data and the current capabilities of the proposed infield system to come with an optimized set of preplots. These preplots, along with supporting documentation, are presented to the acquisition team prior to infield operations.
Part of the Osprey suite of 4D tools
Undershoot Planning
There are a number of drivers that may impact undershoot planning: cost, targeting offsets, reducing azimuthal differences, minimizing the hole, repeating a previous undershoot. To help the decision making process, RIL have developed software that has been used to analyse standard to very complex undershoots.
An undershoot project might include,
- The best methodology: standard undershoot, oblique undershoot, repeat undershoot, post installation undershoot
- The optimal geometry of the passes: source/streamer vessel placement, streamer length, number of streamers
- Infield considerations: contractor safety limits, infrastructure, exclusion zones, vessel hardware
- Real world modeling: currents, feather
From the modeling, RIL create an infield undershoot plan in the form of preplots, detailed powerpoint presentations and additional supporting documentation. An open dialogue with the infield team will assist the infield process and facilitate quick changes to the plan caused by unforseen infield operations. The image below shows a modelling/analysis session underway using a mixture of Osprey Undershoot and ArcGIS.
